Computer systems may include several memory units coupled to a memory controller. The memory controller may transmit control, address, and clock signals to the memory units. In some systems, the memory units are coupled to the controller using one or more signal trees, where a conductive connector coupling the controller to the memory units branches out from the controller to each memory unit. Generally, the branches of the tree structure are split approximately equally to each memory unit to maintain a uniform amount of capacitance at each branch. However, as the tree structure gets longer to reach more memory units, more branches are added, so that the capacitance of the tree structure itself increases. The speed of signal transmission through the tree structure may be limited by the amount of capacitance presented by the structure, because a driver in the memory controller must drive the entire tree structure to transmit signals to the memory units.
Accordingly, as memory speeds increase, a daisy chain wiring configuration may be used. An example of memory units connected to a controller using a daisy chain wiring configuration is shown in FIG. 1. A controller 100 is coupled to memory units 110, 120, 130, and 140 by a daisy chain 150. The daisy chain 150 is coupled from the controller 100 to the memory units 110, 120, 130, and 140 sequentially. Address, command, and clock signals transmitted from the controller 100 may accordingly be propagated by the daisy chain to each of the memory units 110, 120, 130, and 140.
In the daisy chain configuration shown in FIG. 1, inductance and impedance are distributed in lumped elements along the daisy chain, with each of the memory units 110, 120, 130, and 140 presenting a capacitance to the daisy chain 150. Due in part to the lumped nature of the elements and the distributed load along the daisy chain 150, increased bandwidth may be achieved relative to the tree configuration described above. In some designs, the distances between the memory units 110, 120, 130, and 140 are carefully specified to improve signal quality along the daisy chain.